1. Field of the Invention
The present invention relates generally to processes and apparatuses for finishing workpieces, and in particular, processes and apparatuses for surface-finishing.
2. Description of the Related Art
Tubular members often have surfaces that require surface-finishing. Tubular members are used to form luminal prostheses that have lumens defining fluid pathways. Stents are one type of luminal prosthesis that can be placed in various types of body vessels, such as body vessels of the vasculature system (e.g., blood vessels), respiratory system, and gastrointestinal system. Arterial stents, for example, can support dissections in arterial tissue that may occur during medical procedures, such as balloon angioplasty procedures intended to maintain fluid pathways. To support weakened or damaged blood vessels, stents may be used to form stent grafts, which are in turn used to support the blood vessels.
A stent with a lattice structure can serve as a scaffold for engaging a body vessel to maintain vessel patency. The lattice structure of an expandable stent provides for expansion from a collapsed configuration for delivery to an expanded configuration for implantation. The lattice structure can be formed by a plurality of struts, beams, or ribs often made of stainless steel, nickel titanium alloy, and other biocompatible materials.
Various types of fabrication processes are used to form the lattice structure that provides the desired functionality. However, these fabrication processes can result in contamination (e.g., buildup of foreign matter) and in the formation of an unwanted stent topography, which may include relatively rough or sharp edges, hanging burrs, or other surface irregularities. After forming the lattice structure, the stent may therefore require further processing to obtain a desired surface-finish. Mechanical machining is one type of fabrication process that often leads to the formation of outwardly extending burrs (e.g., burrs extending either radially inward or outward). Laser cutting processes often produce stents with rough surfaces along cutouts as well as an appreciable amount of unwanted material, such as slag particles. Other conventional cutting techniques used to form complicated lattice structures tend to suffer from similar problems.
Surface-finishing processes are performed to obtain the desired surface topography (e.g., surface smoothness) to improve the stent's performance when implanted in a subject. Rough edges or protuberances of an arterial stent, for example, may facilitate the formation of thrombus and ultimately lead to closing of the stent's lumen, clot formation, damage to arterial walls, stenosis, and other undesirable conditions. Unfortunately, additional medical procedures may need to be performed to, for example, further expand the stent, remove unwanted accumulated material, replace the stent, or combat stenosis.
The stent's topology may also be unsuitable for many delivery techniques. Balloon expandable stents are often deployed using a controllably inflatable balloon (e.g., an angioplasty balloon) made from a thin material suitable for containing a pressurized inflation fluid, such as saline. Unfortunately, uneven surfaces, rough or sharp edges, burrs, debris, or similar structures may puncture and rupture the balloon when the balloon is inflated outwardly against the sidewall of the stent. Accordingly, these types of destructive features on the stent have to be removed before expanding the stent.
Mechanical surface-finishers, such as rough files, are often used to perform surface-finishing processes. To remove inwardly extending burrs, a rough file is inserted into the lumen of the stent and used to break off or wear down the burrs. Because stents have relatively narrow lumens, it is often difficult to insert such files into the lumens, let alone to manipulate the files to produce the desired surface-finish. Additionally, large burrs may block the lumens and thus make it difficult to insert and advance the files through the lumens. Even if a file can be inserted into a stent's lumen, the file can damage or break the stent's sidewall during surface-finishing, especially if the sidewall is relatively thin.
Chemical surface-finishing is also unsuitable for producing a desired topography because it removes material from all the exposed surfaces of the stent. For example, if a chemical surface-finisher is employed to remove large burrs, it may remove significant amounts of material from all the surfaces to which it is exposed, thus significantly altering the overall geometry of the stent. It is also difficult to control the uniformity of the stent's geometry when utilizing chemical surface-finishers.
The present disclosure is directed to overcome one or more of the shortcomings set forth above, and provide further related advantages.